Last fall, long before the first vote was cast in the Democratic presidential contest, Rep. Rahm Emanuel of Illinois told me in an interview that he thought Barack Obama could beat Hillary Rodham Clinton. But Emanuel added an important proviso, saying Obama could win only "if he runs a perfect campaign."

Emanuel, a former aide in the Clinton White House and a fellow Chicagoan of Obama's, is now happily clinging to neutrality because as chairman of the House Democratic Caucus, he is part of the congressional leadership.

A veteran campaign strategist himself, Emanuel said he knew it was rare that a first-time national candidate like Obama could achieve perfection. He could point to the experiences of such diverse figures as Hubert Humphrey, Ronald Reagan, Al Gore, George H.W. Bush (and now John McCain), all of whom ran losing campaigns for their parties' nominations before finally winning.

He clearly implied that odds were that Obama would not run "a perfect campaign." And this week Emanuel was proved right.

When Obama, after 12 victories in a row (including Tuesday's win in Vermont), stumbled in Texas, Ohio and Rhode Island, he allowed Clinton back into the race.

In pulling off her third comeback — following her recovery after losses in Iowa and South Carolina — Clinton proclaimed at a Columbus rally that her victory was vindication for everyone "who's ever been counted out but refused to be knocked out and for everyone who has stumbled but stood right back up." Signaling her intention to fight on to the August convention in Denver, she said, "We're going on, we're going strong and we're going all the way."

Obama, in San Antonio, responded by boasting plausibly that the net results of Tuesday's voting would hardly dent his roughly 150-vote lead in elected delegates, a lead that is likely to grow in upcoming contests in Wyoming and Mississippi.

But by adding Texas and Ohio to her previous wins in California, New York and New Jersey, Clinton strengthened her argument to the superdelegates who may ultimately decide this contest that she is the stronger bet in the big states that are key to Democratic victories in November. She is the early favorite in the next big battleground, Pennsylvania, on April 22. Its Democratic governor, Ed Rendell, told me 10 days ago that she would certainly win there if she came in off victories in Ohio and Texas.

The most striking thing in the exit polls was Clinton's success with the late deciders. Among the one-fifth of the voters who told exit polls they made their decision during the last three days, Clinton led by 21 points in Texas and 18 points in Ohio.

In that time span, Obama was pummeled by all sides, and he did not stand up well. McCain also took him to task for a statement implying that al-Qaida was not already embedded in Iraq. His own campaign was caught in contradictions about a senior adviser's private assurances to the Canadian government not to take too seriously Obama's talk about renegotiating NAFTA. Reporters pestered him so persistently with questions about his past ties to a Chicagoan on trial for political fixing that Obama bolted from the room.

Important as these events were, the overriding factor in Clinton's comeback may have been the wish by Democratic voters, who admire both these candidates, to see the contest continue. A Washington Post-ABC News poll reported Tuesday morning showed that two-thirds of the Democrats wanted Clinton to stay in if she won either Texas or Ohio.

As they contemplate a campaign against McCain, who emphasizes his national security credentials, the superdelegates must factor in the fact that in both these big states, Democrats gave much higher marks to Clinton than to Obama as a potential commander in chief.

Whenever the Democratic race ends, the winner is on notice that the tougher struggle lies ahead. In claiming the Republican nomination, McCain signaled his readiness to defend his position on Iraq, pledging to bring the war "to the swiftest possible conclusion," but only after defeating al-Qaida in Iraq so America can leave with "our honor intact."

And Mike Huckabee, in his graceful concession speech, signaled the growing Republican unity behind McCain, while strengthening his own claim to a future leadership role in the GOP.

This has been a magnificent campaign on both sides. And the best of it may still lie ahead.